Probably not much. I don't know how fast a PicassoIV is but your CPU really will be the bottleneck with Quake and Quake 2.
Actually, GLQuake and Quake 2 will get a tremendous speed boost through Warp3D compared to the software only option of using a PicassoIV.
On my 50Mhz 68060, ClickBOOM Quake only becomes playable in a small-ish window with 2x2 pixels, however GLQuake gets reasonable frame rates in all modes from 320x240 right up to 1024x768 (640x480 being about the best mode to use on my setup).